I've pretty much standardized on the URC-8810 remotes. But I decided to get a few URC-6011 and URC-6012 remotes off of eBay. The RemoteChart.pdf says these are JP1 remotes but are missing the connector pins.

I soldered the connecting pins into each remote and for the life of me, I can't get the software to see them or do anything with them. I believe they should be able to use the same JP1 cable (a USB JP1.2 with a JP1.2 to JP1 converter) as my URC-8810 remotes. But no matter what I try, I get the 'Remote not found' message. I've tried no batteries. I've tried very weak batteries. And of course I've tried new batteries. I've also tried talking to them in JP1.2 mode without the converter.

It's obvious these URC-6011 and URC-6012 remotes are setup for JP1. After all, they have the six pin header on the circuit board. And everything else (except for a few missing keys) are the same as the URC-8810 remote. (And I've verified I can read and write to my URC-8810 remotes.)

Can anybody give me some guidance? I would really like to get these remotes to do their thing!

But those remotes also lack the EEPROM chip needed for programming. So you need to obtain and solder in those chips as well. You have unwittingly taken on a larger and more complex and expensive project than you thought. Even though each chip is only 35 cents, shipping is $8. If you want to pursue it further, this is what you'll need to do:

Like your 8810, the 6011 and 6012 are both at least 14 years old. Additionally, they require rather extensive modification to work with JP1. Tell us what features you like, and perhaps we can recommend a newer model known to work without any soldering and possibly without even using a JP1 cable at all (standard USB instead).

Update: I unsoldiered the EEPROM chips. And was very careful to have no excess soldier anywhere. All three of the URC-6011 remotes did 4 short blinks when I gave them the Setup-981 command. And in fact, I've programmed them with RMIR and two of the work.

But the third one is acting like it isn't seeing any buttons being pressed. I noticed it was blinking its Red LED as if a button was being pressed even when nothing was being pressed. I took it apart, and used alcohol on a Q-Tip to clean all the contact areas. Well... That must have been a bad thing to do because now it isn't blinking the Red LED as if a button is pressed, but it isn't acknowledging anything when a button (including SETUP) is pressed.

I suspect I've destroyed that remote. But can anybody tell me what happened?

It's possible you've just got a stuck button after reassembly. I'd crack it back open, make sure the button sheet is clean on the contact side and properly aligned. Low batteries can also result in strange blinking.